This invention relates to surgical retractors, particularly to sternal retractors used primarily in internal mammary artery (IMA) dissection.
To gain access to an internal mammary artery, a surgeon must split the patient's sternum and raise and retract one side of the rib cage. Many devices are known in the art which accomplish this. Typical designs comprise a toothed crossbar, a fixed arm attached to one end of the crossbar in a perpendicular orientation, and another arm, approximately parallel to the first, which may be moved along the crossbar with a crank mechanism to alter the spread of the arms. Each of the arms has a retractor blade attached near its end that is used to make contact with the sternum.
Many variations from this basic design exist in the art and are intended at least in part to help regulate the magnitude and direction of the force applied to sternum. If the spreading or lifting force is applied unevenly, nerve and tissue damage, as well as cracked ribs can result. A common variation is in the design of the retractor blades which vary in size, shape, and freedom of motion. The art also includes various designs for frames that connect the retractor mechanism to a fixed object such as an operating table to provide leverage and stability.
Many designs use a straight crossbar, which has one disadvantage. These retractors exert force in only one plane, that which is parallel to ground level during surgery, i.e. they provide a spreading force but no lifting force. To lift the sternum, a tilting force must be applied to the crossbar manually. This can cause excessive, uneven forces and undesirable stress concentrations at contact points.
Several alterations to the straight crossbar are known. One design (U.S. Pat. No. 5,088,472) utilizes a crossbar that is curved in the plane that is parallel to ground level during use. The arms are positioned on the concave side of the crossbar when the retractor is used below the chest, and positioned on the convex side when the retractor is used above the chest. This design gives the arms a non-parallel orientation and creates a variation in the spread width from one end of the retractor blades to the other. As a result, the more flexible lower ribs are spread at a rate greater than the upper ribs, lessening the chance for injury. However, the insufficient lifting force problem remains because the crossbar is curved only in a plane parallel to ground level.
Another design (U.S. Pat. No. 5,772,583) has its crossbar is bent downward so that it approximately conforms to the patient's body during use. This design is meant to reduce interference with the surgeon's field of movement, but it fails to provide a sufficient lifting force. In fact, this design creates a downward force that is less desirable than the force created by the average straight crossbar.
Designs that use a frame attached to a fixed object are more stable and generally direct the force more advantageously. However, they are inherently more complicated, and their bulk can interfere with the movement and vision of the surgical team.